Masks come into their own when used with Photoshop's "Alpha Channels" -
a powerful method of applying and manipulating masks by turning them
into selection areas. By using channel operations you can create a
wide range of effects, for example applying globes to any bitmapped
image, such as a photograph. You will find four masks on your
GlobeShots disc: a circle mask to make pasting a globe into a
background easier, and three cloud masks for giving your globes a
more realistic effect. The masks are all high resolution, and you
will find them in a folder in the High Resolution Globes folder.

Placing a globe on a background

With a high resolution GlobeShots image open, click on the
right-pointing arrow at top right of the "Channels" floating
palette (make the palette visible by selecting "Show Channels"
from the "Window" menu), and select "New Channel..." or click on
the New Channel icon at the bottom of the palette. In the dialog
box which appears, name the channel "Mask." Click "OK." The image
window now shows the new channel as solid black.

Now open the circle mask, Select All, and drag the mask into
the globe mask channel that you just created. You can now close
the mask window.

Make the RGB channel of your globe image visible by clicking on
"RGB" in the Channels window.

Choose "Load Selection..." from the "Select" menu, and then
choose "Copy" from the "Edit" menu. You have now copied the globe,
without its background, to the clipboard. You can now paste the
globe onto any other image of your choice, such as a photograph or
piece of art.

Applying a cloud mask

Follow steps 1 - 3 in "Placing a Globe on a Background. Then:

Choose "Load Selection..." from the "Select" menu, and then hit
the "Delete" key, first making sure that the background color is
set to white. Alternatively, rather than deleting to white, you can
use the "Brightness/Contrast" controls to apply white to the clouds.